I've been successfully reloading 5.7 now for the past few weeks and have had quite a bit of success in the pistol.

I've been reloading 1x brass with ~5.0 of True Blue and a 50 gr bullet. Worked up from 4.0 gr with iffy/weak cycling. Firm recoil now, feels good.

Light primer cratering, and ~50% of the brass showed signs of neck separation. (Shiny Band) some of the 1x 197 even showed banding, and I think I should throw them away? A little bummed, thought it was tougher than this. Hear people getting ~5 reloads. Maybe a lighter bullet is easier on it? I also think TB has initially too high of a pressure spike, but still burns too slow, producing a huge muzzle flash, what's a better speed powder?

Thankfully we got Jay to save us with this stronger brass. I got 400? I was gonna give a go soon.

I was hoping I might be able to get a cutaway of both brass to see the changes in the sidewall construction.

I'm guessing because of the lower case capacity I should reduce loads by ~25%? To start out.

Let's see pictures of your brass. I've got some that appears to have a band forming at the shoulder/neck junction, but it turned out to be lacquer damage right at that point, brass was fine. Maybe you've got something similar going on.